The proposed research will continue to elucidate the multiple factors which control myocardial perfusion. As in the past, the aim of this work is to answer questions important in defining the physiology and pathophysiology of coronary blood flow in animal models which are closely akin to man in a physiologic state. Thus, this work will be carried out in awake animal models. The research proposal contains two specific aims: 1) beat-to-beat regulation of coronary blood flow, and 2) physical, pharmacologic and neural factors which affect atrial blood flow.